DeRhamComputation/sage/superelliptic/decomposition_into_g0_g8.sage

def decomposition_g0_g8(fct, prec = 50):
    '''Writes fct as a difference g0 - g8, with g0 regular on the affine patch and g8 at the points in infinity.'''
    C = fct.curve
    g = C.genus()
    coord = fct.coordinates()
    nontrivial_part = 0*C.x
    for i, a in enumerate(C.cohomology_of_structure_sheaf_basis()):
        nontrivial_part += coord[i]*a
    fct -= nontrivial_part
    if fct.coordinates(prec=prec) != g*[0]:
        raise ValueError("The given function cannot be written as g0 - g8.")
    
    Fxy, Rxy, x, y = C.fct_field
    fct = Fxy(fct.function)
    num = fct.numerator()
    den = fct.denominator()
    aux_den = superelliptic_function(C, Rxy(den))
    g0 = superelliptic_function(C, 0)
    g8 = superelliptic_function(C, 0)
    for monomial in num.monomials():
        aux = superelliptic_function(C, monomial)
        if aux.expansion_at_infty().valuation() >= aux_den.expansion_at_infty().valuation():
            g8 += num.monomial_coefficient(monomial)*aux/aux_den
        else:
            g0 += num.monomial_coefficient(monomial)*aux/aux_den
    return (g0, g8, nontrivial_part)

def decomposition_omega0_omega8(omega, prec=50):
    '''Writes omega as a difference omega0 - omega8, with omega0 regular on the affine patch and omega8 at the points in infinity.'''
    C = omega.curve
    omega.form = reduction(C, omega.form)
    F = C.base_ring
    delta = C.nb_of_pts_at_infty
    m = C.exponent
    if sum(omega.residue(place = i, prec = 50) for i in range(delta)) != 0:
        raise ValueError(str(omega) + " has non zero residue!")
    Fxy, Rxy, x, y = C.fct_field
    Rx.<x> = PolynomialRing(F)
    Fx = FractionField(Rx)
    fct = Fxy(omega.form)
    num = fct.numerator()
    den = fct.denominator()
    aux_den = superelliptic_function(C, Rxy(den))
    g0 = superelliptic_function(C, 0)
    g8 = superelliptic_function(C, 0)
    for j in range(0, m):
        component = Fx(omega.jth_component(j))
        q, r = component.numerator().quo_rem(component.denominator())
        g0 += (C.y)^(-j)*superelliptic_function(C, Rxy(q))
        if ((C.y)^(-j)*superelliptic_function(C, Fxy(r/component.denominator()))*C.dx).expansion_at_infty().valuation() < 0:
            raise ValueError("Something went wrong for "+str(omega))
        g8 -= (C.y)^(-j)*superelliptic_function(C, Fxy(r/component.denominator()))
    g0, g8  = g0*C.dx, g8*C.dx
    if g0.is_regular_on_U0():
        return (g0, g8)
    #Rx.<x> = PolynomialRing(F)
    #Rx.<x> = PolynomialRing(F)
    #aux_fct = (g0.form)*y
    else:
        raise ValueError("Something went wrong for "+str(omega) +". Result would be "+str(g0)+ " and " + str(g8))